U.S. patent number 9,246,537 [Application Number 14/435,283] was granted by the patent office on 2016-01-26 for method for determining the arrival time of a uwb pulse and corresponding receiver.
This patent grant is currently assigned to BE SPOON, Commissariat a l'energie atomique et aux energies alternatives. The grantee listed for this patent is BE SPOON, Commissariat a l'energie atomique et aux energies alternatives. Invention is credited to Francois Dehmas, Gilles Masson, Laurent Ouvry.
United States Patent |
9,246,537 |
Dehmas , et al. |
January 26, 2016 |
Method for determining the arrival time of a UWB pulse and
corresponding receiver
Abstract
A method for determining arrival time of a UWB pulse at a
receiver. When a pulse is modulated at an RF frequency, the
receiver includes a quadrature demodulator, a first correlating
stage for correlating the in-phase signal with the first and second
signals of an orthogonal base on a time window and a second
correlating stage for correlating the quadrature signal with the
first and second signals of the orthogonal base on the same window,
a phase estimator estimating the phase of the signal received in
the orthogonal base from the correlation results of the first
and/or second correlating stage(s), and a computing device
determining the arrival time from the phase thus estimated.
Inventors: |
Dehmas; Francois (Vif,
FR), Masson; Gilles (Renage, FR), Ouvry;
Laurent (Grenoble, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Commissariat a l'energie atomique et aux energies alternatives
BE SPOON |
Paris
Bourget du Lac |
N/A
N/A |
FR
FR |
|
|
Assignee: |
Commissariat a l'energie atomique
et aux energies alternatives (Paris, FR)
BE SPOON (Bourget du Lac, FR)
|
Family
ID: |
47989066 |
Appl.
No.: |
14/435,283 |
Filed: |
October 10, 2013 |
PCT
Filed: |
October 10, 2013 |
PCT No.: |
PCT/EP2013/071127 |
371(c)(1),(2),(4) Date: |
April 13, 2015 |
PCT
Pub. No.: |
WO2014/060278 |
PCT
Pub. Date: |
April 24, 2014 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150295620 A1 |
Oct 15, 2015 |
|
Foreign Application Priority Data
|
|
|
|
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Oct 16, 2012 [FR] |
|
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12 59861 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
1/7183 (20130101); H04B 1/69 (20130101); H04B
1/06 (20130101); H04B 2001/6908 (20130101); H04B
2201/71634 (20130101) |
Current International
Class: |
H04B
1/69 (20110101); H04B 1/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
US. Appl. No. 14/435,370, filed Apr. 13, 2015, Dehmas, et al. cited
by applicant .
U.S. Appl. No. 14/435,283, filed Apr. 13, 2015, Dehmas, et al.
cited by applicant .
U.S. Appl. No. 14/435,338, filed Apr. 13, 2015, Ouvry, et al. cited
by applicant .
U.S. Appl. No. 14/739,072, filed Jun. 15, 2015, Dehmas, et al.
cited by applicant .
Bautista, et al., "Low power beamforming RF architecture enabling
fine ranging and AOA techniques", IEEE International Conference on
Ultra-Wideband, (Sep. 14, 2011), pp. 585-589, XP 032115737. cited
by applicant .
Heiries, et al., "UWB Backscattering System for Passive RFID Tag
Ranging and Tracking", IEEE International Conference on
Ultra-Wideband, (Sep. 14, 2011), pp. 489-493, XP 032115715. cited
by applicant .
Masson, et al., "A 1 nJ/b 3.2-to-4.7 GHz UWB 50 Mpulses/s Double
Quadrature Receiver for Communication and Localization", IEEE,
(2010), pp. 502-505. cited by applicant .
International Search Report Issued Jan. 20, 2014 in PCT/EP13/071127
Filed Oct. 10, 2013. cited by applicant .
French Search Report Issued Jun. 12, 2013 in Application No. FR
1259861 Filed Oct. 16, 2012. cited by applicant.
|
Primary Examiner: Ha; Dac
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. A method for determining the arrival time of a UWB pulse at a
receiver, comprising: (a) receiving a UWB signal containing the
pulse; (b) correlating the signal thus received with a first signal
and a second signal making up an orthogonal base to obtain
respectively a first projection value on the first signal and a
second projection value on the second signal, the correlation being
carried out on a time window of duration T; wherein: (c) the first
and second signals are two quadrature versions of a same periodical
signal of period 2T; (d) the phase of the received signal is
estimated in the orthogonal base from the first and second
projection values; (e) an arrival time of the pulse is determined
from the phase thus estimated.
2. The method for determining the arrival time of a UWB pulse
according to claim 1, wherein the phase of the signal received in
the orthogonal base is obtained by .PHI..function. ##EQU00036##
where AI is the first projection value and AQ is the second
projection value.
3. The method for determining the arrival time of a UWB pulse
according to claim 1, wherein the UWB signal is modulated at a
carrier frequency, and a translation into baseband of the signal
received in (a) is carried out to obtain an in-phase signal and a
quadrature signal with a local oscillator at the carrier frequency,
and the signal received in (b)is correlated by carrying out: (b1)a
first correlation of the in-phase signal with the first and second
signals of the orthogonal base to obtain respectively first and
second projection values, the correlation being carried out on the
detection window of duration T; (b2) a second correlation of the
quadrature signal with the first and second signals of the
orthogonal base to obtain respectively third and fourth projection
values, the correlation being carried out on the window of duration
T; (d1) the phase of the signal received in the orthogonal base
being estimated from the first and second projection values and/or
third and fourth projection values.
4. The method for determining the arrival time of a UWB pulse
according to claim 3, wherein the phase of the signal received in
the orthogonal base is estimated by .PHI..function. ##EQU00037##
where II is the first projection value and IQ is the second
projection value.
5. The method for determining the arrival time of a UWB pulse
according to claim 3, wherein the phase of the signal received in
the orthogonal base is estimated by .PHI..function. ##EQU00038##
where QI is the third projection value and QQ is the fourth
projection value.
6. The method for determining the arrival time of a UWB pulse
according to claim 3, wherein the phase of the signal received in
the orthogonal base is estimated by: .PHI..function. ##EQU00039##
if the energy of the in-phase signal, in the detection window, is
higher than the energy of the quadrature signal, in the same
window; .PHI..function. ##EQU00040## in the reverse case; where II
, IQ, QI , QQ are respectively the first, second, third and fourth
projection values.
7. The method for determining the arrival time of a UWB pulse
according to claim 1, wherein the first and second signals of the
orthogonal base are respectively given by
.function..function..times..pi..times..times..beta..times..times..times..-
times..function..function..times..pi..times..times..beta.
##EQU00041## where .beta. is any phase.
8. The method for determining the arrival time of a UWB pulse
according to claim 1, wherein the first and second signals of the
orthogonal base are respectively given by
e.sub.1(t)=e(t-t.sub..beta.) and
e.sub.2(t)=e(t-T/2-t.sub..beta.)where t.sub..beta. is any time and
e(t)is the function defined by e(t)=+1 if 0.ltoreq.t<T and
e(t)=-1 if T.ltoreq.t<2T.
9. A receiver for determining the arrival time of a UWB pulse
comprising: a correlating stage for correlating a signal received
by the receiver with a first signal and a second signal making up
an orthogonal base to obtain respectively a first projection value
on the first signal and a second projection value on the second
signal, the correlation being carried out on a detection window of
duration T; wherein: the first and second signals are two
quadrature versions of a same periodical signal of period 2T; the
receiver further comprising: a phase estimator estimating the phase
of the signal received in the orthogonal base from the first and
second projection values; computing means for determining an
arrival time of the pulse from the phase thus estimated.
10. The receiver according to claim 9, wherein the phase estimator
estimates the phase by .PHI..function. ##EQU00042## where AI is the
first projection value and AQ is the second projection value.
11. The receiver according to claim 9, wherein the UWB pulse is
modulated at a carrier frequency, and the receiver further
comprises: a quadrature demodulator including a local oscillator,
the demodulator translating into baseband the signal received by
the receiver to obtain an in-phase signal and a quadrature signal
with the local oscillator; the correlating stage comprising: a
first stage on the in-phase channel for correlating the in-phase
signal with the first and second signals of the orthogonal base to
provide respectively the first and second projection values, and a
second stage on the quadrature channel for correlating the
quadrature signal with the first and second signals of the
orthogonal base to provide respectively the third and fourth
projection values; the phase estimator estimating the phase of the
signal received in the orthogonal base from the first and second
projection values and/or third and fourth projection values.
12. The receiver according to claim 11, wherein the estimator
estimates the phase by .PHI..function. ##EQU00043## where II is the
first projection value and IQ is the second projection value.
13. The receiver according to claim 11, wherein the estimator
estimates the phase by .PHI..function. ##EQU00044## where QI is the
third projection value and QQ is the fourth projection value.
14. The receiver according to claim 11, wherein the estimator
estimates the phase by: .PHI..function. ##EQU00045## if the energy
of the in-phase signal, in the integration window, is higher than
the energy of the quadrature signal, in the same window;
.PHI..function. ##EQU00046## in the reverse case; where II , IQ, QI
, QQ are respectively the first, second, third and fourth
projection values.
15. The receiver according to claim 9, wherein the first and second
signals of the orthogonal base are respectively given by
.function..function..times..pi..times..times..beta..times..times..times..-
times..function..function..times..pi..times..times..beta.
##EQU00047## where .beta. is any phase.
16. The receiver according to claim 9, wherein the first and second
signals of the orthogonal base are respectively given by
e.sub.1(t)=e(t-t.sub..beta.) and
e.sub.2(t)=e(t-T/2-t.sub..beta.)where t.sub..beta. is any time and
e(t) is the function defined by e(t)=+1 if 0.ltoreq.t<T and
e(t)=-1 if T .ltoreq.t<2T.
17. The receiver according to claim 9, wherein the first and second
signals of the orthogonal base are respectively given by:
.function..function..times..pi..times..times..beta..times..times..times..-
times..function..function..times..pi..times..times..beta.
##EQU00048## where .beta. is any phase, when the pulse width is
lower than a predetermined threshold; and by
e.sub.1(t)=e(t-t.sub..beta.) and
e.sub.2(t)=e(t-T/2-t.sub..beta.)where t.sub..beta. is any time and
e(t) is the function defined by e(t)=+1 if 0.ltoreq.t<T and
e(t)=-1 if T.ltoreq.t<2T, when the pulse width is higher than
the threshold.
Description
TECHNICAL FIELD
The present invention relates to the field of UWB (Ultra Wide Band)
receivers and more particularly the synchronization of such
receivers.
STATE OF PRIOR ART
Pulsed type ultra-wide band (UWB) telecommunication systems are
well known in the state of the art. In such a system, a symbol
emitted by a transmitter is transmitted using a sequence of
ultra-short pulses, in the order of one nanosecond or one hundred
picoseconds.
FIG. 1A schematically illustrates the signal emitted by a UWB
transmitter, corresponding to a given information symbol. This
signal consists of pulses being repeated with a period T.sub.c.
The signal emitted by the transmitter, in the absence of a
modulation by modulation symbols, can be expressed in the following
way:
.function..times..times..function..times..function..times..pi..times..tim-
es..function..phi. ##EQU00001## where p(t) is the form of the unit
pulse into baseband, f.sub.0 is the carrier frequency, .phi..sub.0,
the phase at the origin, and T.sub.c is the repetition period. The
duration .tau. of the unit pulse p(t) is substantially lower than
the duration of the period T.sub.c.
This base signal can be amplitude and/or position modulated to
transmit one symbol per frame consisting of a given number of
repetition periods. The frame is of duration T.sub.f=LT.sub.c where
L is the number of periods in the frame. For example, if the
modulation is a Pulse Position Modulation (PPM), the modulated
signal can be expressed in the form:
.function..times..times..function..times..function..times..pi..times..tim-
es..function..phi. ##EQU00002## where .epsilon. is a modulation
delay substantially lower than the period T.sub.c and m=0, . . . ,
M-1 is the PPM M-ary position of the symbol.
In a similar way, a symbol can be transmitted by the UWB
transmitter by means of an amplitude or phase modulation at which
the modulated signal can then be expressed in the form:
.function..times..times..times..function..times..function..times..pi..tim-
es..times..function..phi. ##EQU00003## where .alpha..sub.m is the
symbol to be transmitted, for example a PAM (Pulse Amplitude
Modulation) or (D)BPSK ((Differential) Binary Phase Shift Keying)
symbol.
To separate the transmissions of different transmitters, it can be
considered that each transmitter is associated with a given time
hopping code c.sub.k, k=0, . . . , L-1, c.sub.k.epsilon.{0, . . . ,
L-1}, with the proviso that the codes relating to different
transmitters are orthogonal. FIG. 1B illustrates the non-modulated
signal of a transmitter using a time hopping code. When it is
modulated by a position modulation or amplitude modulation, the
signal transmitted is respectively written as:
.function..times..times..function..times..times..times..times..function..-
times..pi..times..times..function..times..times..phi..function..times..tim-
es..times..function..times..times..function..times..pi..times..times..func-
tion..phi. ##EQU00004##
Regardless of the modulation type used, the receiver must precisely
determine the arrival time of the UWB pulses received. Indeed, the
receiver does not generally a priori know in which time windows the
UWB pulses appear (lack of synchronization reference and, if any,
ignorance of the time hopping code used). Additionally, when a PPM
(Pulse Position Modulation) is used, the arrival time of the pulse
carries the modulation information and must consequently be
precisely determined.
A theoretical method for determining the arrival time of a UWB
pulse consists in carrying out a correlation of this signal with a
succession of local replica of the pulse, offset in time, in other
words a sliding correlation. However, such a method is not feasible
in practice because the brevity of the pulse would impose to carry
out a very high number of correlations, even for a relatively short
time window, for example in the order of a few hundred ns.
Patent application EP-A-1580901 provides a method for detecting the
arrival time of a pulse in a time window which does not require a
sliding correlation to be carried out.
The principle of this method is illustrated in FIG. 2. It uses a
UWB receiver 200 comprising a first baseband demodulation stage 210
followed, for each of the I and Q channels, by a correlation stage
with two quadrature low frequency sine curves. More precisely, the
quadrature mixer 220 carries out a projection of the in-phase
signal, noted s.sub.I, on a base consisting of two low frequency
orthogonal sine curves. In a similar way, the quadrature mixer 220
carries out a projection of the quadrature signal on this same
base. The signals obtained by projection, noted s.sub.II,s.sub.IQ
for the channel I and s.sub.QI,s.sub.QQ for the channel Q are
integrated inside a time window (called integration time window
hereinafter) in the integrators 230. Optionally, the integration
results are accumulated on a plurality of time windows, separated
by the repetition period of the UWB signal or offset according to a
time hopping code. The integrated signals are quadratically summed
in 235, 240 and the sum thus obtained is compared with a threshold
value in 250. If the sum obtained exceeds the threshold value, the
receiver concludes that a pulse has been received in the time
window.
The UWB receiver 200 however does not enable a UWB pulse to be
located in the integration time window.
The article of G. Masson et al. entitled "A 1 nJ/b 3.2 to 4.7 GHz
UWB 50 Mpulses/s double quadrature receiver for communication and
localization" published in Proc. of the ESSCIRC 2010, 14-16 Sep.
2010, pp. 502-505, describes the architecture of such a receiver
and mentions the possibility of using correlation signals with low
frequency sine curves to deduce the arrival time (ToA) of the UWB
pulse in the integration time window. However, the correlation
signals of the channels I and Q, that is s.sub.II, s.sub.IQ for the
channel I and s.sub.QI,s.sub.QQ for the channel Q do not enable the
arrival time to be unambiguously determined.
Therefore, the purpose of the present invention is to provide a
method for precisely estimating the arrival time of a UWB pulse in
an integration time window which does not require a sliding
correlation and which is not affected by any ambiguity.
DISCLOSURE OF THE INVENTION
The present invention is defined by a method for determining the
arrival time of a UWB pulse at a receiver, comprising the following
steps of:
(a) receiving a UWB signal containing said pulse;
(b) correlating the signal thus received with a first signal and a
second signal making up an orthogonal base to obtain respectively a
first projection value on said first signal and a second projection
value on said second signal, the correlation being carried out on a
time window of duration T;
said method further comprising the following steps:
(c) the first and second signals are two quadrature versions of a
same periodical signal of period 2T;
(d) the phase of the received signal is estimated in the orthogonal
base from the first and second projection values;
(e) the arrival time of said pulse is determined from the phase
thus estimated.
Advantageously, the phase of the signal received in the orthogonal
base is obtained by
.PHI..function. ##EQU00005## where AI is the first projection value
and AQ is the second projection value.
According to one embodiment, since the UWB signal is modulated at a
carrier frequency, a translation into baseband of the signal
received in step (a) is carried out to obtain an in-phase signal
and a quadrature signal with a local oscillator at said carrier
frequency, and the signal received in step (b) is correlated by
carrying out:
(b1) a first correlation of the in-phase signal with the first and
second signals of the orthogonal base to obtain respectively first
and second projection values, the correlation being carried out on
the detection window of duration T;
(b2) a second correlation of the quadrature signal with the first
and second signals of the orthogonal base to obtain respectively
third and fourth projection values, the correlation being carried
out on the window of duration T;
(d1) the phase of the signal received in the orthogonal base being
estimated from the first and second projection values and/or third
and fourth projection values.
Advantageously, the phase of the signal received in the orthogonal
base is estimated by
.phi..function. ##EQU00006## where II is the first projection value
and IQ is the second projection value.
Alternatively, the phase of the signal received in the orthogonal
base can be estimated by
.phi..function. ##EQU00007## where QI is the third projection value
and QQ is the fourth projection value.
Further alternatively, the phase of the signal received in the
orthogonal base is estimated by:
.phi..function. ##EQU00008## if the energy of the in-phase signal,
in the detection window, is higher than the energy of the
quadrature signal, in the same window;
.phi..function. ##EQU00009## in the reverse case; where II, IQ, QI,
QQ are respectively the first, second, third and fourth projection
values.
According to a first alternative of the orthogonal base, the first
and second signals of the orthogonal base are respectively given
by
.function..function..times..pi..times..times..beta..times..times..times..-
times..function..function..times..pi..times..times..beta.
##EQU00010## where .beta. is any phase.
According to a second alternative of the orthogonal base, the first
and second signals of the orthogonal base are respectively given by
e.sub.1(t)=e(t-t.sub..beta.) and e.sub.2(t)=e(t-T/2-t.sub..beta.)
where t.sub..beta. is any time and e(t) is the function defined by
e(t)=+1 if 0.ltoreq.t<T and e(t)=-1 if T.ltoreq.t<2T.
The invention also relates to a receiver for determining the
arrival time of a UWB pulse comprising: a correlation stage for
correlating a signal received by the receiver with a first signal
(e.sub.1) and a second signal (e.sub.2) making up an orthogonal
base to obtain respectively a first projection value on said first
signal and a second projection value on said second signal, the
correlation being carried out on a detection window of duration T,
the first and second signals are two quadrature versions of a same
periodical signal of period 2T;
the receiver further comprises: a phase estimator for estimating
the phase of the signal received in the orthogonal base from the
first and second projection values; computing means for determining
the arrival time of said pulse from the phase thus estimated.
The phase estimator advantageously estimates the phase by means
of
.PHI..function. ##EQU00011## where AI is the first projection value
and AQ is the second projection value.
When the UWB pulse is modulated at a carrier frequency, the
receiver can further comprise: a quadrature demodulator including a
local oscillator, said demodulator translating into baseband the
signal received by the receiver to obtain an in-phase signal and a
quadrature signal with said local oscillator; the correlating stage
comprising:
a first stage on the in-phase channel for correlating the in-phase
signal with said first and second signals of the orthogonal base to
provide respectively said first and second projection values,
and
a second stage on the quadrature channel for correlating the
quadrature signal with said first and second signals of the
orthogonal base to provide respectively said third and fourth
projection values;
the phase estimator estimating the phase of the signal received in
the orthogonal base from the first and second projection values
and/or third and fourth projection values.
The estimator can estimate the phase by means of
.phi..function. ##EQU00012## where II is the first projection value
and IQ is the second projection value.
Alternatively, the estimator can estimate the phase by means of
.phi..function. ##EQU00013## where QI is the third projection value
and QQ is the fourth projection value.
Further alternatively, the estimator can estimate the phase by
means of:
.phi..function. ##EQU00014## if the energy of the in-phase signal,
in the integration window, is higher than the energy of the
quadrature signal, in the same window;
.phi..function. ##EQU00015## in the reverse case; where II, IQ, QI,
QQ are respectively the first, second, third and fourth projection
values.
According to a first alternative of the orthogonal base, the first
and second signals of the orthogonal base are respectively given
by
.function..function..times..pi..times..times..beta..times..times..times..-
times..function..function..times..pi..times..times..beta.
##EQU00016## where .beta. is any phase.
According to a second alternative of the orthogonal base, the first
and second signals of the orthogonal base are respectively given by
e.sub.1(t)=e(t-t.sub..beta.) and e.sub.2(t)=e(t-T/2-t.sub..beta.)
where t.sub..beta. is any time and e(t) is the function defined by
e(t)=+1 if 0.ltoreq.t<T and e(t)=-1 if T.ltoreq.t<2T.
According to a third alternative of the orthogonal base, the first
and second signals of the orthogonal base are respectively given
by:
.function..function..times..pi..times..times..beta..times..times..times..-
times..function..function..times..pi..times..times..beta.
##EQU00017## where .beta. is any phase, when the pulse width is
lower than a predetermined threshold; and by
e.sub.1(t)=e(t-t.sub..beta.) and e.sub.2(t)=e(t-T/2-t.sub..beta.)
where t.sub..beta. is any time and e(t) is the function defined by
e(t)=+1 if 0.ltoreq.t<T and e(t)=-1 if T.ltoreq.t<2T, when
the pulse width is higher than said threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics and advantages of the invention will appear
upon reading a preferential embodiment of the invention made in
reference to the appended figures in which:
FIG. 1A, already described, represents an exemplary pulsed type UWB
signal;
FIG. 1B, already described, represents an exemplary pulsed type UWB
signal coded by a time hopping code;
FIG. 2, already described, schematically represents the structure
of a UWB receiver enabling the presence of a UWB pulse to be
detected in a time window;
FIG. 3A schematically represents a UWB receiver according to a
first embodiment of the invention;
FIG. 3B schematically represents a UWB receiver according to a
second embodiment of the invention;
FIG. 4A represents a first function for estimating the arrival time
for the receiver of FIG. 3A;
FIG. 4B represents a second function for estimating the arrival
time for the receiver of FIG. 3A.
DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS
A receiver intended to receive a pulsed UWB signal will be
considered in the following. This pulsed signal can be coded by a
time hopping code or not, being non-modulated or modulated by
modulation symbols belonging to a position, amplitude or phase
modulation alphabet or other.
It will be assumed in the following that the receiver has to
determine the arrival time of a pulse inside a given time window.
As indicated in the introducing part, this will in particular be
the case when the receiver attempts to be synchronized on the UWB
signal, when it attempts to correct a clock drift, or looks for a
time hopping code used by the transmitter of this signal. This will
also be the case in the context of a distance measurement by a UWB
transceiver, the distance being obtained from the arrival time of
the UWB signal reflected on the target the distance of which is
desired to be measured.
Generally, the UWB pulse the arrival time of which is attempted to
be determined can be approximated in the following form:
.function..times..function..times..pi..times..times..function..alpha..tim-
es..function..tau. ##EQU00018## where A.sub.t is the amplitude of
the pulse emitted, f.sub.0 is the center frequency of the pulse,
that is the carrier frequency, t.sub.0 the instant corresponding to
the pulse peak, .alpha. is the pulse phase at the time t.sub.0 and
.tau. is the pulse width, supposed to be Gaussian. Generally, the
pulse width is defined as the reverse of the width of the pass-band
at 3 dB.
FIG. 3A represents a UWB receiver according to a first embodiment
of the invention.
This receiver comprises a UWB antenna 300, an RF filter followed by
a low noise amplifier 320.
The signal received by the receiver, thus filtered and amplified,
is translated into baseband by the quadrature demodulator 330 using
a local oscillator at the carrier frequency f.sub.0.
The signals obtained on the channels I and Q of the demodulator 330
are filtered in the low pass filters 340 before being correlated in
351-354 with signals e.sub.1 and e.sub.2 forming an orthogonal
projection base with the meaning given later.
More precisely, if I(t) and Q(t) are the in-phase and quadrature
signals, after filtering, the correlators 351 and 352 carry out a
correlation of the in-phase signal respectively with a first signal
and a second signal making up the orthogonal projection base,
namely:
.intg..times..function..times..function..times..times.d.intg..times..func-
tion..times..function..times..times.d ##EQU00019## where W is the
integration time window.
In a similar way, the correlators 353 and 354 carry out a
correlation of the quadrature signal respectively with the first
signal and the second signal of the orthogonal projection base,
namely:
.intg..times..function..times..function..times..times.d.intg..times..func-
tion..times..function..times..times.d ##EQU00020##
Signals II,IQ,QI,QQ from the correlators are digitized and
processed by a phase estimator 360. The computing means 370 deduce
the arrival time of the UWB pulse from the phase estimated in
360.
Signals e.sub.1 and e.sub.2 are chosen to be orthogonal in that
they satisfy:
.intg..times..function..times..function..times..times.d
##EQU00021##
Signals e.sub.1 and e.sub.2 are obtained from a periodic function e
having as a period twice the width of the integration time window,
both signals being in quadrature signals, that is offset by a
quarter of said period. The width of the integration time window
will be noted T in the following.
According to a first alternative, said periodic function is a
sinusoidal function, for example
.function..function..times..pi..times..times. ##EQU00022## the
quadrature signals e.sub.1 and e.sub.2 being obtained as
follows:
.function..function..times..pi..times..times..beta..times..times..functio-
n..function..times..pi..times..times..beta..times..times.
##EQU00023## where .beta. is any phase. Since the integration time
window W (of width T) only contains a half-period of the signals
e.sub.1 and e.sub.2, the orthogonal base is referred to as a
half-period sinusoidal one.
According to a second alternative, said periodical function is a
square clock of period 2T, for example such that: e(t)=+1 if
0.ltoreq.t<T and e(t)=-1 if T.ltoreq.t<2T (13) the quadrature
signals e.sub.1 and e.sub.2 being obtained as follows:
e.sub.1(t)=e(t-t.sub..beta.) (14-1)
e.sub.2(t)=e(t-T/2-t.sub..beta.) (14-2) where t.sub..beta. is any
time. Since the integration time window W (of width T) only
contains a half-period of the signals e.sub.1 and e.sub.2, the
orthogonal base is referred to as a half-slot one.
It will be readily verified that signals e.sub.1 and e.sub.2
according to the first or second alternative are actually
orthogonal with respect to the relationship (11).
Without loss of generality, the phase estimator and the computing
means will be explained hereinafter for both alternatives
contemplated above.
The in-phase signal I(t), at the input of the correlators 351-352,
and the quadrature signal Q(t), at the input of the correlators
353-354 can be expressed in the following form:
.function..times..function..times..pi..times..times..times..theta..times.-
.function..tau..times..times..function..times..function..times..pi..times.-
.times..times..theta..times..function..tau..times..times.
##EQU00024## where A.sub.r is the amplitude of the signal received,
depending on A.sub.t and on the attenuation of the propagation
channel, and .theta. is the phase of the signal received, depending
on the phase of the signal emitted, .alpha., on the characteristics
of the propagation channel, and on the local oscillator phase used
for translating into baseband.
For the sake of simplifying the computations, it will be assumed
that the propagation time between the transmitter and the receiver
is null and that the integration time window is [0,T], with the
proviso that the following conclusions hold true for any
propagation time.
According to a first alternative embodiment, the half-period
sinusoidal base defined by the expressions (12-1) and (12-2) is
used as the orthogonal base.
The projection on this orthogonal base is carried out by the
correlators 351-354. At the output of these correlators, there is
respectively obtained:
.intg..times..times..function..times..pi..times..times..beta..times..func-
tion..times..pi..times..times..times..theta..times..function..tau..times.d-
.times..times..intg..times..times..function..times..pi..times..times..beta-
..times..function..times..pi..times..times..times..theta..times..function.-
.tau..times.d.times..times..intg..times..times..function..times..pi..times-
..times..beta..times..function..times..pi..times..times..times..theta..tim-
es..function..tau..times.d.times..times..intg..times..times..function..tim-
es..pi..times..times..beta..times..function..times..pi..times..times..time-
s..theta..times..function..tau..times.d.times..times.
##EQU00025##
The expressions (16-1) to (16-4) can be gathered using a complex
form:
.times.I.times..times..times..times..function..times..pi..times..times..t-
imes..theta..times..intg..times..function.I.function..times..pi..times..ti-
mes..beta..tau..times..times.d.times..times..times.I.times..times..times..-
times..function..times..pi..times..times..times..theta..times..intg..times-
..function.I.function..times..pi..times..times..beta..tau..times..times.d.-
times..times. ##EQU00026## or, more simply: ZI=A.sub.r
cos(2.pi.f.sub.0t.sub.0+.theta.)z (18-1) ZQ=-A.sub.r
sin(2.pi.f.sub.0t.sub.0+.theta.)z (18-2) with:
.pi..times..tau..function..pi..times..times..tau.I.function..times..pi..t-
imes..times..beta..function..function..tau.I.times..pi..times..times..tau.-
.times. ##EQU00027## where erf(.) is the complex error
function.
The phase estimator 360 estimates the phase
.phi.=arg(ZI)=arg(ZQ)=arg(z) (modulo .pi.) of the baseband signal
in the orthogonal base (e.sub.1,e.sub.2) by means of:
.phi..function..times..times. ##EQU00028## or alternatively, by
means of:
.phi..function..times..times. ##EQU00029##
It will be noted that both estimators {circumflex over
(.phi.)}.sub.I and {circumflex over (.phi.)}.sub.Q both give an
estimation of the phase .phi.. However, depending on the value of
the phase 2.pi.f.sub.0t.sub.0+.theta., the energy of the UWB pulse
can be carried rather by the signal ZI or by the signal ZQ, as
shown by the expressions (18-1) and (18-2).
Either of the estimators can be advantageously selected depending
on the energy
|ZI|.sup.2=A.sub.r.sup.2|z|.sup.2cos.sup.2(2.pi.f.sub.0t.sub.0+.th-
eta.) and
|ZQ|.sup.2=A.sub.r.sup.2|z|.sup.2sin.sup.2(2.pi.f.sub.0t.sub.0+.-
theta.). In other words, if the energy P.sub.I of the signal on the
in-phase channel, in the integration time window, is higher than
the energy P.sub.Q of the signal on the quadrature channel, in the
same window, the estimator {circumflex over (.phi.)}.sub.I will be
selected. The estimator {circumflex over (.phi.)}.sub.Q will be
selected in the reverse case. There will thus always be the benefit
of the best signal to noise ratio for the phase estimation. In
other words, in this case this will be taken as the estimator:
{circumflex over (.phi.)}={circumflex over (.phi.)}.sub.I if
P.sub.I>P.sub.Q {circumflex over (.phi.)}={circumflex over
(.phi.)}.sub.Q if P.sub.I.ltoreq.P.sub.Q (21) The estimators
{circumflex over (.phi.)}.sub.I and {circumflex over
(.phi.)}.sub.Q, and hence the estimator {circumflex over (.phi.)},
are injective functions of the time window (here [0,T]) in the
phase space ([-.pi./2,.pi./2]), in other words the estimators in
question enable the arrival time to be unambiguously obtained,
unlike prior art. These injective functions will be respectively
noted g.sub.I(t),g.sub.Q(t),g(t). At an estimated phase
({circumflex over (.phi.)}.sub.I,{circumflex over
(.phi.)}.sub.Q,{circumflex over (.phi.)}), the arrival time of the
UWB pulse can be unequivocally deduced by means of the reverse
function (g.sub.I.sup.-1,g.sub.Q.sup.-1,g.sup.-1).
Returning to FIG. 3A, the phase estimator 360 determines from
values II,IQ and/or values QI,QQ coming from the correlators
351-354 the phase of the baseband signal thanks to one of the
estimators {circumflex over (.phi.)}.sub.I,{circumflex over
(.phi.)}.sub.Q,{circumflex over (.phi.)}.
The computing means 370 deduce therefrom, thanks to the
abovementioned reverse function
(g.sub.I.sup.-1,g.sub.Q.sup.-1,g.sup.-1), the arrival time of the
UWB pulse. The computing means can comprise a look-up table of the
reverse function or an approximation by intervals of said
function/reverse function. Alternatives to the computing means can
be contemplated by those skilled in the art without departing from
the scope of the present invention.
FIG. 4A represents the evaluation of the phase estimator
{circumflex over (.phi.)} as a function of the arrival time of the
pulse (here the time t.sub.0 corresponding to the maximum of the
UWB pulse), for different band widths (and thus different pulse
widths .tau.).
The numerical values used in the expressions (18-1), (18-2) and
(19) for the example of FIG. 4A are: f.sub.0=4 GHz, T=2 ns;
t.sub.0=1 ns; A.sub.r=1; .theta.=0; att.sub.dB=-10 dB;
.beta.=-.pi./2. It will be noted that a different value of .beta.
simply results in an offset of the estimation function {circumflex
over (.phi.)} in time.
It will be noticed that FIG. 4A actually represents the estimation
function {circumflex over (.phi.)} beyond the integration time
window [0,T], more precisely with a T/2 margin on either side of
this window. It is thus observed that when the center of the pulse
"comes out" of the window but the pulse has a high overlapping
degree with the same, the phase estimator {circumflex over
(.phi.)}(t) also enables the arrival time (thus located outside the
window) to be detected satisfactorily. However, when the
overlapping decreases, the estimation is degraded because of the
low signal to noise ratio (low values of the energies |ZI|.sup.2
and |ZQ|.sup.2).
According to a second alternative embodiment, the half-slot base
defined by the expressions (14-1) and (14-2) is used as the
orthogonal base.
The projection on this orthogonal base is carried out by the
correlators 351-354. At the output of these correlators, and in the
same hypotheses as for the first alternative, the signals are
respectively obtained: II=A.sub.r
cos(2.pi.f.sub.0t.sub.0+.theta.)x' (22-1) IQ=A.sub.r
cos(2.pi.f.sub.0t.sub.0+.theta.)y' (22-2) QI=A.sub.r
sin(2.pi.f.sub.0t.sub.0+.theta.)x' (22-3) QQ=A.sub.r
sin(2.pi.f.sub.0t.sub.0+.theta.)y' (22-4) with:
'.pi..times..tau..function..tau..function..tau..times..times..times..time-
s.'.pi..times..tau..times..function..tau..function..tau..function..tau..ti-
mes..times. ##EQU00030##
The expressions (22-1) to (22-4) can be gathered using a complex
form, and noting z'=x'+iy': ZI=II+iIQ=A.sub.r
cos(2.pi.f.sub.0t.sub.0+.theta.)z' (24-1) ZQ=QI+iQQ=A.sub.r
sin(2.pi.f.sub.0t.sub.0+.theta.)z' (24-2)
As for the first alternative, the phase estimator 360 estimates the
phase .phi.'=arg(ZI)=arg(ZQ)=arg(z') (modulo .pi.) of the baseband
signal in the orthogonal base (e.sub.1,e.sub.2) by means of the
expression (20-1), (20-2) or (21), the estimators being
respectively noted {circumflex over (.phi.)}'.sub.I,{circumflex
over (.phi.)}'.sub.Q,{circumflex over (.phi.)}'.
The estimators {circumflex over (.phi.)}'.sub.I and {circumflex
over (.phi.)}'.sub.Q, and hence the estimator {circumflex over
(.phi.)}', are also injective functions of the time window (here
[0,T]) in the phase space ([-.pi./2,.pi./2]). They thus can be
reversed on the image of [0,T], the reverse functions of
{circumflex over (.phi.)}'.sub.I,{circumflex over
(.phi.)}'.sub.Q,{circumflex over (.phi.)}' being respectively noted
g'.sub.I.sup.-1,g'.sub.Q.sup.-1,g'.sup.-1.
The phase estimator 360 determines from the values II,IQ and/or
values QI,QQ coming from the correlators 351-354 the phase of the
baseband signal thanks to one of the estimators {circumflex over
(.phi.)}'.sub.I,{circumflex over (.phi.)}'.sub.Q,{circumflex over
(.phi.)}'.
The computing means 370 deduce therefrom, thanks to the
abovementioned reverse function
(g'.sub.I.sup.-1,g'.sub.Q.sup.-1,g'.sup.-1), the arrival time of
the UWB pulse.
FIG. 4B represents the time course of the phase estimator
{circumflex over (.phi.)}' as a function of the arrival time of the
pulse under the same conditions as previously. The numerical values
are the same as those of the example in FIG. 4A, with in addition
t.sub..beta.=0.
As for FIG. 4A, it is noticed that the arrival time (here t.sub.0)
of the UWB pulse can be determined, including when the peak comes
out of the integration time window. This latter conclusion is
however only valid under the proviso that the pass-band of the
signal is relatively low (relatively wide pulse consequently
overlapping the integration time window).
It will be noted that the curve of the estimator {circumflex over
(.phi.)}' has a linearity zone more reduced than that of the
estimator {circumflex over (.phi.)} in the center zone of the
window. As a result, for excursions of the arrival time which are
higher than a threshold value, the estimation using the half-slot
base will be of a lesser accuracy than that using the half-period
sinusoidal base. On the other hand, for low excursions, the
accuracy will be better since the slope in the linearity zone is
steeper.
It is clear for those skilled in the art that other orthogonal
bases can be contemplated given that the signals making up this
base are obtained from a periodical function e having as a period
twice the width of the integration time window, said signals being
selected in quadrature.
In particular, "intermediate" bases between the half-period
sinusoidal base and the half-slot base can be obtained by filtering
more or fewer harmonics of the half-slot base using a low pass
filtering.
Advantageously, a set of orthogonal bases will be available and
they will be adaptively used depending on the band width of the UWB
signal (width of the UWB pulse). Thus, when the band width is low
(wide pulse), the half-slot base will be preferably used and when
the band width is high (narrow pulse), the half-period sinusoidal
base will be used, so as to keep a same sensitivity whatever the
band width.
In the embodiment described above, only a single UWB pulse
appearing in a time window has been considered. However, when the
UWB signal is periodical or when the successive pulses obey a time
code, a plurality of time windows separated by the signal of the
UWB signal or offset by the time code can be contemplated. The
correlation results obtained on the different windows are then
advantageously accumulated at the output of each correlator before
being provided to the phase estimator 360.
According to a second embodiment, more particularly relating to a
wired transmission, the UWB pulse the arrival time of which is
attempted to be determined, is not modulated by a RF carrier but
transmitted into baseband, in other words:
.function..times..function..tau. ##EQU00031## with the same
notation conventions as previously. In this case, the UWB receiver
does not carry out a translation into baseband by means of a
quadrature demodulator at the carrier frequency but directly
projects the signal received on the orthogonal base.
FIG. 3B represents a UWB receiver according to a second embodiment
of the invention. Elements bearing the same reference numerals as
those of FIG. 3A are identical or similar to those already
described.
More precisely, the receiver comprises an antenna 330, a band-pass
filter 310, a low noise amplifier 330. The filtered and amplified
signal, r(t) is correlated in 351 and 352 with the signals e.sub.1
and e.sub.2 as defined above.
Keeping the previous notations, at the output of the correlators
351, 352, the signals are respectively obtained:
.intg..times..function..times..function..times..times.d.times..times..int-
g..times..function..times..function..times..times.d.times..times.
##EQU00032##
The signals AI,AQ are digitized and processed by a phase estimator,
360. This estimator estimates the phase of the signal received r(t)
in the orthogonal base (e.sub.1,e.sub.2). The computing means 370
determine the arrival time of the UWB pulse from the phase thus
estimated.
The orthogonal base will be successively contemplated according to
the first and second alternatives, as for the first embodiment.
If the orthogonal base is half-period sinusoidal, signals AI,AQ are
expressed in the form:
.intg..times..times..function..times..pi..times..times..beta..times..func-
tion..tau..times.d.times..times..intg..times..times..function..times..pi..-
times..times..beta..times..function..tau..times.d.times..times.
##EQU00033## Or even, by assuming a complex notation:
Z=AI+iAQ=A.sub.rz (28) where z is defined in (19).
The phase estimator 360 estimates the phase .phi.=arg(Z)=arg(z) of
the baseband signal in the orthogonal base (e.sub.1,e.sub.2) by
means of:
.PHI..function. ##EQU00034##
The function {circumflex over (.phi.)} is injective of the time
window in the phase space. Therefore, it can be reversed on the
image of this window in the phase space. The computing means 370
use this reverse function, G.sup.-1, to determine unambiguously the
arrival time of the UWB pulse.
If the orthogonal base is a half-slot base, the signals at the
output of the correlators 351 and 352 are respectively expressed
as: AI=A.sub.rx' (30-1) AQ=A.sub.ry' (30-2) and in complex
notation: Z=AI+iAQ=A.sub.rz' (31) where x' and y' have been defined
in (23-1) and (23-2).
As for the first alternative, the phase estimator 360 estimates the
phase .phi.'=arg(Z)=arg(z') of the baseband signal in the
orthogonal base (e.sub.1,e.sub.2) by means of
.PHI.'.function. ##EQU00035## Since the function {circumflex over
(.phi.)}' is once again injective of the time window in the phase
space, it can be reversed on the image of the window. The computing
means 370 use this reverse function, G'.sup.-1, to determine
unambiguously the arrival time of the UWB pulse.
The alternatives relating to the accumulation on several successive
windows are applicable as for the first embodiment without needing
to further detail them herein.
* * * * *